1. Field of the Invention
The present invention relates to a method of making NiFeCoxe2x80x94Oxe2x80x94N or NiFeCoxe2x80x94N films for shields and/or poles of a magnetic head and, more particularly, to a method of employing unique process conditions in a DC magnetron for forming such films.
2. Description of the Related Art
The heart of a computer is an assembly that is referred to as a magnetic disk drive. The magnetic disk drive includes a rotating magnetic disk with write and read heads that are suspended by a suspension arm above the rotating disk. An actuator swings the suspension arm, placing the write and read heads over selected circular tracks on the rotating disk. The write and read heads are directly mounted on a slider that has an air bearing surface (ABS). The suspension arm biases the slider into contact with the surface of the disk when the disk is not rotating. When the disk rotates, air is swirled by the rotating disk adjacent the ABS of the slider, causing the slider to ride on an air bearing a slight distance from the surface of the rotating disk. When the slider rides on the air bearing, the write and read heads are employed for writing magnetic impressions to and reading magnetic impressions from the rotating disk. The read and write heads are connected to processing circuitry that operates according to a computer program to implement the writing and reading functions.
The write head includes a coil layer embedded in insulation layers (insulation stack) with the insulation stack being sandwiched between first and second pole piece layers (P1 and P2). A gap is formed between the first and second pole piece layers by a nonmagnetic gap layer at the air bearing surface (ABS) of the write head. The pole piece layers are connected at a back gap. Current conducted to the coil layer induces a magnetic field into the pole pieces that fringes across the gap between the pole pieces at the ABS. The fringe field writes information in tracks on moving media, such as in circular tracks on a rotating disk.
In recent read heads, a spin valve sensor is employed for sensing magnetic fields from the rotating magnetic disk. The sensor includes a nonmagnetic conductive layer, hereinafter referred to as a spacer layer, sandwiched between first and second ferromagnetic layers, hereinafter referred to as a pinned layer, and a free layer. First and second leads are connected to the spin valve sensor for conducting a sense current therethrough. The magnetization of the pinned layer is pinned perpendicular to an air bearing surface (ABS) of the head and the magnetic moment of the free layer is located parallel to the ABS but free to rotate in response to external magnetic fields. The magnetization of the pinned layer is typically pinned by exchange coupling with an antiferromagnetic layer. A spin valve sensor is sometimes referred to as a giant magnetoresistive (GMR) sensor. When a spin valve sensor employs a single pinned layer it is referred to as a simple spin valve sensor. In the read head the spin valve sensor is located between first and second read gap layers and the read gap layers are located between first and second shield layers (S1 and S2).
The shield layers (S1, S2) and pole piece layers (P1, P2) are in close proximity to the read sensor. Because of this proximity, it is important that the layers be magnetically stable. In order to achieve this, the shield or pole layers are formed by plating or sputter deposition in the presence of a magnetic field that is parallel to the ABS in the plane of the shield or pole layer. The field orients the easy axis (e.a.) of the shield or pole layer in the direction of the field, namely parallel to the ABS and in the plane of the shield or pole layer. This orientation also means that the magnetic domains in the shield or pole layer in the vicinity of the sensor are also aligned with their longitudinal axes parallel to the ABS in the plane of the shield or pole layer. It is important that these domains retain their orientation as formed and not move around when subjected to extraneous fields such as fields from the write head or fields from the rotating magnetic disk. When these magnetic domains move, noise is generated which is referred to in the art as Barkhausen noise. This noise seriously degrades the read signal of the read head. Further, if the magnetic domains do not come back to their original position, the shield or pole layer exerts a differently oriented field on the free layer of the spin valve sensor. This changes the magnetic bias on the free layer causing read signal asymmetry.
There are numerous materials which may be used in the construction of shield layers (S1 and S2) and pole piece layers (P1 and P2), the most common being NiFe. Nickel iron (NiFe), with a composition typically of approximately Ni81Fe19 (wt. %), is a soft magnetic material that provides good shielding of the spin valve sensor from magnetic fields except within the read gap where signals are sensed by the sensor. Nickel iron (NiFe) also has near zero magnetostriction so that after lapping the head to form the ABS there is near zero stress induced anisotropy. Unfortunately, however, nickel iron (NiFe) has a low intrinsic magnetic anisotropy (HK). Intrinsic magnetic anisotropy is the amount of applied field required to rotate the magnetic moment of the layer 90 degrees from an easy axis orientation. The intrinsic magnetic anisotropy of nickel iron (NiFe) is 2-5 oersteds (Oe). After the first shield layer (S1) and second shield layer (S2) layer are formed, they are subjected to unfavorable magnetic fields that are required in subsequent processing steps. The insulation layers of the insulation stack, which are typically photoresist layers, are hard bake annealed in the presence of a magnetic field which is directed perpendicular to the ABS for the purpose of maintaining the magnetic spins of the antiferromagnetic pinning layer in the spin valve sensor oriented in a direction perpendicular to the ABS. The hard bake anneals are typically at least three high temperature anneals with each anneal typically being performed at around 232xc2x0 C. for 400 minutes. These annealing steps reduce the anisotropy field HK of nickel iron (NiFe) to very low values of 0-1 Oe.
The field typically employed for maintaining the spins of the pinning layer during hard bake of the insulation stack is about 1500 Oe. Because of the low intrinsic magnetic anisotropy of a nickel iron (NiFe) shield layer, for instance, the aforementioned anneals in subsequent processing steps can cause the easy axis and the magnetic domains of the shield layer to switch their orientation such that they are no longer parallel to the ABS. The magnetic field present in these anneals reduces or destroys the intrinsic anisotropy field that was created in the nickel iron (NiFe) when it was originally formed and may create an anisotropy field perpendicular to the ABS. This is a very unfavorable orientation for magnetic domains of a shield layer. When the shields are subjected to perpendicular fields from the write head during the write function or subjected to perpendicular fields from the rotating magnetic disk the magnetic domains will move. This causes Barkhausen noise which degrades the read signal and causes a potential change in biasing of the spin valve sensor which results in read signal asymmetry.
Some shield materials such as Sendust that require high temperature (475xc2x0 C.) annealing on the easy axis can withstand subsequent hard axis annealing at 230-270xc2x0 C. Others such as plated 80/20 NiFe or CoTaZr have been shown to be stabilized to some degree by an initial anneal on the easy axis at a higher temperature, such as 280xc2x0 C., than will be encountered during later processing. This strategy may be workable for S1, which is formed before the GMR sensor, but not for S2, which must be made after the GMR sensor has been deposited. Annealing on the easy axis is not acceptable for many exchange materials employed in GMR sensors. Other materials considered for write head and shield materials, such as FeN, FeAIN, FeTaN, FeZrN, FeRuN and CoTaZr reduce or even switch HK in conventional processing.
In general, it is desirable to minimize the reduction of HK that occurs in hard axis annealing, and it is particularly desirable that this be done while simultaneously achieving low hard axis coercivity, HCH, and near zero magnetostriction xcex for the process conditions used for the GMR wafers. Accordingly, there is a strong-felt need for a material for the first shield layer (S1), the second shield (S2) and first and second pole piece layers (P1 and P2) that will remain sufficiently stable after being subjected to heat and magnetic fields employed in subsequent process steps without pre-annealing along the easy axis.
I employ NiFeCo alloys (approximately (Ni0.81Fe0.19)100-XCoX (wt %), where 0.5 less than X less than 25) for increasing HK. These alloys have HK in the range of 5-25 Oe as-deposited or after easy axis annealing. It has been found, however, that NiFeCo films sputtered under a variety of conditions all lose anisotropy, and in some cases switch their easy axis direction, when subjected to the hard axis annealing conditions in the present hard bake anneal process (232xc2x0 C., 400 min). In addition, thick sputtered NiFeCo films (1-2 xcexcm), even those with near-zero magnetostriction, have vertical anisotropy. It is desirable to improve sputtered NiFeCo films so they possess high anisotropy, low coercivity, and in-plane anisotropy after GMR head processing.
I have found that doping NiFeCo with N2O or N2 greatly increases HK after hard axis annealing and that when laminated with, for example, alumina or silica, thick structures can be sputter deposited with excellent in-plane anisotropy. Approximately 1.8 xcexcm thick films were sputter deposited on Al2O3xe2x80x94TiC ceramic substrates with lapped undercoat alumina from a target with composition Ni73.2Fe18.1Co8.7 (wt %) in a Balzers Z660 sputtering system using DC magnetron at a power of 1750 W, gas pressure of 2.0xc3x9710xe2x88x923 mbar, and no substrate bias. The gas was a mixture of Ar and either N2O or N2. After deposition, the films were annealed three times on the hard axis at 232xc2x0 C. for 400 min in a magnetic field of approximately 1500 Oe. A typical film after annealing had an HK of 10.8 Oe with in-plane anisotropy.
An object of the present invention is to provide a method of making high uniaxial anisotropy HK films after hard axis annealing.
Another object is to provide a method of making the foregoing films with low hard axis and easy axis coercivities and low magnetostriction.
A further object is to provide a method of making the foregoing films into unique laminations which are especially useful for second pole piece layers of a write head.
Other objects and attendant advantages of the invention will be appreciated upon reading the following description taken together with the accompanying drawings.